My mechanic neighbor just got a 84 F-150 w/300-6 for a temporary plow truck, until he replaces the transmisison in his main truck. Anyways the thing will not idle, and it runs horribly.

It is a feedback carb with the EGR disabled. For the hell of it, i disconnected the vacuum line off the Map sensor (the vacuum was not steady, and pulsed crazily, could have been because he had to keep his foot on the gas a bit to keep it idling) and blocked the vacuum line so it wouldn't leak, but the engine did not run one bit different at all. I thought that was kind of odd, so i disconnected the MAP's harness connector, because i know the computer will just use default fuel settings, and that too made no differnce in its running.

One thing I noticed is that by the carb was a circular 4 pin connector, with 3 pins filled. It looks just like the back-fire injector harness connector on my 87 EFI 2.9 ranger. Couldn't find anywhere for it to go, so just left it hanging, any ideas where this would go?

Also, the wires going to the ODB connector coroded out and fell out of the connector, can someone tell me which color wire goes where on the connector, so we can attempt to pull the codes.

For some odd reason as well, the guy who had the truck first, put in an electric fuel pump, by passing the mechanical one. Any ideas why one might do this intsead of just replaciong the mechanical pump?

And finally, would a feedback carb engine run if the computer was not working or disconnected?

 

Just eliminated the electronic crap on my 84 F150.Converted to DS2 and an earlier non feedback carby.Runs great.The DS2 system is plug and play,as the computer system uses a completely stand alone harness from the truck harness.The way that I removed the computer crap from mine was this.Remove the gang plug from the computer under the dash.It is basically right below the steering coloumn.Cut the wires from the plug,and pull them out through the firewall under the hood.Go to either a salvage yard or your favorite parts house and get the DS2 distributer,control box,wires,cap and rotor.If you buy new,you will have to go to a salvage yard to get the wiring harness that goes from the control box to the coil and the distributer.The control box should have the BLUE strain grommet.

Leo

 

Thats not really an option, he is just using it as a beater to plow until he gets his other trucks up again. I mean, it wouldn't be a problem as he has 30+ years of mechanic expeperience under his belt. But this issue is really odd.

You mention something about a control box? On the paasenger side fender wall, there is this little box with wires plugged into it that says "Car Quest Engine Controls". Any idea what his might be?

Also, would a feedback carb system run at all with a bad computer, or is the spark also computer controlled?

 

Ok.The box that controls the ignition system is USUALLY located on the drivers side inner fender.For mine I ran an extra ground wire from one of the box mount bolts to the firewall.It is appx 6" square,and has two sets of wires coming out of it with some sockets attached.
As for the carby,I don`t think that it would do well without the electronics hooked up.I think the "carquest engine controls"unit is the starter solenoid.
Leo

 

Its not the solenoid, the guy said it was the alternators regulator. I'm not sure though, I'd thought by 84 the alts had internal regulation?

 

I have a 84 F250 4x4 with the same(used to have) setup, I just pulled the SPOUT connector to the TFI modual and ran on base timeing(bumped up a little) then pulled the wire harness off the carb, it ran like that till I switched to EFI. Also check the power valve in the carb, that thing will cause a lot of problems too.

 

External voltage regulators were around for a while after 84 IIRC.Personally,I much prefer the separate VR.It is a lot less expensive to purchase one or the other(VR or alternator)that to have to replace and alternator because the VR crapped out.

Leo

 

We found that the carb is missing the throttle position sensor, whichi is what im guessing the round 3 pin connector would go to.

Can someone tell me where the feedback actuator is on the carb?

Also, if I unplug the connector from the distributor, what will fire the spark?

 

Your Distrubitor is a TFI system, Close by the dist connector is a pigtail with a plug inline, that is the SPOUT connector, just pull that out only and the computer will not be able to control timing. The engine will run at base timing by the TFI modual. Next is disconnect the harness to the carb. This will alow the engine to run to find out if the computer is causing or a engine/carb mechanical problem. Most likely your carb is messed up as parts are missing already.

 

Alright, got that, but about the carb, which connector? Is it the 4pin that goes to the solenoid? or just unplug every wire going ot the carb?

 

By the way,if you do the DS2 conversion,open your plug gap to .050.

Leo

 

I pulled all wires off the carb execpt for the electric choke. I ran my truck like that over 3 years before I got enough parts for EFI installed(another long story...) If the engine runs better, just bump base timing up till you ping under load and back down a tad. that will take some time and driving, just don't over advance it!! For a plow truck this should get it running for the job. If it still acts up, check the carb power valve and float, ect...

 

Has anyone considered that the idling problem might be something as simple as a vacuum leak? It certainly has the classic symptoms.

 

Hes gone over that. There appears to be no vacuum leaks. It seems anything below 2000RPM or so, the engine has a very bad miss in a couple of cylinders. There is lots of black smok coming out the exhaust, indicating its running very rich as well